Excise tax

Suppose that instead of an "excise" tax, the government imposes a sales tax (also known as a "value" tax or an "ad valorem" tax). We know that when an excise tax is placed on consumers, the original demand function,

D

(p), becomes D'(p+t) after the tax is imposed. How does the analysis change in the case of a sales tax? In other words, what is D'now a function of? Does the demand curve simply shift down? (You do not need to solve for a numerical value.)

I don't understand how sales tax would be any different than the excise tax...